cast problem from class to interface

Question

Assembly assembly = Assembly.LoadFrom("Logic\\bin\\Debug\\Logic.dll");
            Type queryManagerType = assembly.GetType("Logic." + HttpContext.Current.Session["lang_name"] + "SearchQueryManager");
            var queryManager = (ISearchQueryManager)Activator.CreateInstance(queryManagerType);


public interface ISearchQueryManager
    {
        IList<Advertisements> ApplyQueries(string searchQuery, int page, int pageSize, string orderBy, out int count);
    }

public class SlovenianSearchQueryManager : ISearchQueryManager
    {
...
}

but i get

Unable to cast object of type 'Logic.SlovenianSearchQueryManager' to type 'Logic.ISearchQueryManager'.

EDIT: whole stacktrace

System.InvalidCastException was unhandled by user code
Message="Unable to cast object of type 'Logic.SlovenianSearchQueryManager' to type 'Logic.ISearchQueryManager'."
Source="ViaMura.Web.Module"
StackTrace: at ViaMura.Web.Module.WebController.GetAdvertismentsByRawQuery(String rawQuery, Int32 page, Int32 pageSize, String orderBy, Int32& count) in D:\PROJEKTI\crawler\WebCrawlerSuite\ViaMura.Web.Module\WebController.cs:line 32 at ViaMura.Web.Module.Views.SearchResultsPresenter.OnResultsLoad(Int32 page, Int32 pageSize, String orderBy) in D:\PROJEKTI\crawler\WebCrawlerSuite\ViaMura.Web.Module\Views\SearchResultsPresenter.cs:line 43 at ViaMura.Web.SearchResults.SearchAdvertisments() in D:\PROJEKTI\crawler\WebCrawlerSuite\ViaMura.Web\SearchResults.aspx.cs:line 155 at ViaMura.Web.SearchResults.Page_Load(Object sender, EventArgs e) in D:\PROJEKTI\crawler\WebCrawlerSuite\ViaMura.Web\SearchResults.aspx.cs:line 149 at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at ViaMura.Web.App_Code.PageControllers.BasePage.OnLoad(EventArgs e) in D:\PROJEKTI\crawler\WebCrawlerSuite\ViaMura.Web\App_Code\PageControllers\BasePage.cs:line 89 at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
InnerException:

EDIT2:

string a1 = typeof (ISearchQueryManager).Assembly.Location;
string a2 = typeof(SlovenianSearchQueryManager).Assembly.Location

give me the same result:

C:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\5438a399\53975f83\assembly\dl3\0f9540b5\15407fe2_5db7cb01\Logic.DLL

but

string a3 = queryManagerType.Assembly.Location;

gives me different path:

D:\PROJEKTI\crawler\WebCrawlerSuite\WebCrawler.Logic\bin\Debug\WebCrawler.Logic.dll

Answer 1

In my experience, type mismatch problems like this are always caused by loading types from two different locations, even if you think they should be getting loaded from the same place.

Compare: Two Types not equal that should be

Try looking at the Assembly.Location property of each type in the debugger:

typeof(ISearchQueryManager).Assembly.Location
typeof(SlovenianSearchQueryManager).Assembly.Location

Answer 2

One possible reason for this happening is that you have this ISearchQueryManager interface defined in two different assemblies which in fact doesn't represent the same type. I see that you are playing with dynamic assembly loading. So the interface you are statically casting to is not the interface implemented by the SlovenianSearchQueryManager class even if it has the same name.